Zayn Malik from One Direction greets fans at the 'One Direction: This Is Us' world premiere. Ian Gavan, Getty Images for Sony Pictures

Fans wait for the arrival of One Direction. Andrew Cowie, AFP/Getty Images

Thousands were on hand for the 'One Direction: This Is Us' premiere. Ian Gavan, Getty Images for Sony Pictures

Simon Cowell does an interview at the 'One Direction: This Is Us' premiere. Ian Gavan, Getty Images for Sony Pictures

One Direction fans take their positions in London's Leicester Square ahead of the premiere of the band's new film 'This Is Us' on Tuesday evening at the Empire Cinema. Dan Kitwoo, Getty Images

Harry Styles, left, of One Direction arrives for the world premiere of their film, 'One Direction: This Is Us' Tuesday in London. The film shows the group in concert at London's O2 Arena, along with fly-on-the-wall footage showing what life is like inside one of the world's biggest bands. Andrew Cowie, AFP/Getty Images